ISO 5518:2007

Overview

ISO 5518:2007 specifies a precise spectrophotometric method for determining the benzoic acid content in fruits, vegetables, and derived products. Benzoic acid is commonly used as a preservative, making its quantification crucial for food safety, quality control, and regulatory compliance. This international standard provides laboratories with a reliable procedure to extract, purify, and measure benzoic acid concentration accurately. However, the method excludes samples containing p-chlorobenzoic acid or cinnamic acid due to their interference with the determination process.

Key Topics

• Scope and Limitations:
  • Applicable to fruits, vegetables, juices, jams, and other derived food products.
  • Not suitable if p-chlorobenzoic acid or cinnamic acid is present because of overlapping absorption spectra and chemical transformations during oxidation.
• Method Principle:
  • The sample is homogenized, acidified, and benzoic acid is extracted using diethyl ether.
  • Alkaline re-extraction and purification by oxidation with acidified potassium dichromate remove interfering substances.
  • Purified benzoic acid is then quantified by UV spectrophotometry, measuring absorbance at key wavelengths (267.5 nm, 272 nm, 276.5 nm).
• Sample Preparation:
  • Liquid, pulpy, thick, and solid products have tailored preparation steps, ensuring representative sampling and accurate analysis.
  • Neutralization with sodium hydrogen carbonate prevents benzoic acid loss by volatilization during processing.
• Reagents and Equipment:
  • Use analytical grade reagents such as tartaric acid, sodium hydroxide, potassium dichromate, and diethyl ether.
  • Essential apparatus includes volumetric flasks, separating funnels, spectrophotometer (UV range), water bath, and analytical balance.
• Calibration and Calculation:
  • Establishes a calibration curve using standard benzoic acid solutions to correlate absorbance with concentration.
  • Results expressed in milligrams per liter (mg/L) or milligrams per kilogram (mg/kg) depending on sampling method.
• Performance and Repeatability:
  • Method offers repeatability with absolute differences not exceeding 10 mg/L or mg/kg in 95% of cases, ensuring reliable routine use.

Applications

• Food Quality Control:
  • Accurate detection of benzoic acid levels in fresh and processed fruits and vegetables to ensure compliance with food safety limits.
• Regulatory Compliance:
  • Enables producers and regulatory agencies to verify preservative concentrations per national and international food legislation.
• Research and Development:
  • Supports studies on preservative efficacy, food shelf life, and formulation improvements in fruit and vegetable products.
• Food Industry Laboratories:
  • Ideal for routine testing of juices, jams, sauces, and frozen products for benzoic acid content to maintain product integrity and consumer safety.

Related Standards

• ISO 2951 - Fruit and vegetable products - Determination of sorbic acid content - Spectrophotometric method
• ISO 6636 - Fruit and vegetable products - Determination of sulphur dioxide content
• ISO 7507 - Fruit and vegetable products - Determination of ascorbic acid content
• Codex Alimentarius - General standards for food additives, including maximum levels for benzoic acid in foods

By following ISO 5518:2007, laboratories ensure the accurate and consistent quantification of benzoic acid, supporting food safety, quality assurance, and regulatory adherence in the international food supply chain.